Thermostatic switch



May 7, 1935. c LAUBENFELS 2,000,398

THERMOSTATIC swITcH FiledJuly 5, 1952 Patented May 7, 1935 UNITED STATESPATENT OFFICE 9 Claims.

This invention relates to improvements in thermostatically controlledswitches, and particularly of the type employing a thermostatic stn'pformed of materials having diiferent thermal co- I eillcient ofexpansion.

The object of my invention is to provide a simple, durable andinexpensive switch for electric circuits having a simple and positivemeans for opening and closing the contact members of the switchcontrolled by a thermostatic strip of the type above described.

The idea of opening and closing electrical contacts by means of themovement of a thermostatic strip caused by temperature variations is notnew. The dimculty with switches actuated by a thermostatic strip lies inthe fact that the strip is slow in its movement, whereas the electricalcontact should be broken suddenly to prevent arcing. It is, therefore,the object of my invention to provide means for mounting thethermostatic strip in such manner that the strip may be placed under ayieldable longitudinal compression strain to cause the strip to be bowedor curved, and in such manner that temperature change will cause thestrip to have a tendency to straighten and to assume the position of astraight line, and on the line of force applied to the strip. Uponfurther movement of the strip, the said yieldable force will then assistin causing the strip to assume an oppositely curved position under aconsiderable tension in addition to that of the strip itself, and toprovide in connection with the thermostatic strip means for actuatingone of the contact members of the switch.

A further object is to provide in a thermostatically controlled switchof the type above described, means for applying longitudinal pressure tothe strip in such manner that the reversed curvature of the strip maytake place without setting up destructive strains in the strip.

A further object is to provide a thermostatic switch so constructed thatit may be adjusted to operate its contact members at difierenttemperatures, and in which the electrical contact members are opened andclosed through a comparatively narrow temperature range, and inconnection therewith means whereby the said temperature range may beeasily and quickly varied at the will of the operator.

A further object is to provide a thermostatic switch utilizing acomposite thermostatic strip of material in connection with a flexibleelement adapted to have pressure applied to it in such a manner that therigidity of the element will be rapidly overcome to provide means forrapidly opening and closing the switch contact members, the pressurenecessary to operate the flexible strip being applied through thethermostatic strip above referred to.

My invention consists in the construction, ar- 5 rangement andcombination of the various parts of the device, whereby the objectscontemplated are attained, as hereinafter more fully set forth, pointedout in my claims, and illustrated in the accompanying drawing, in which:

Figure 1 is a side elevation of one form of my improved switchconstruction.

Figure 2 is an end elevation of same.

Figure 3 is a plan view of another form of my improved switch.

Figure 4 is a detail sectional view taken on the line 4-4 of Figure 3.

Figure 5 is a side elevation of a modified form of the switchillustrated in Figures 3 and 4; and

.Figure 6 is an end elevation of same. 20

Referring to the accompanying drawing, I have used the numeral ID toindicate the base of my improved switch construction which is formedpreferably of insulating material. Supported on the base I0 is a bracketII designed to pivotally support one end of a hub 12, the opposite endof the hub being pivoted in the base l0.

Said hub I2 has a flexible strip of material I3 supported therein. Thedownwardly extending end of the member I3 is provided with an electricalcontact member l4 designed to be engaged by a coacting contact member i5 supported by a spring it, one end of which is rigidly secured to apost IT. A set screw I8 is provided for increasing the pressure of thecontact members l4 and I! when in a closed position.

A set screw 20 is provided for limiting the inward movement of thecontact member IS. The upper end of the strip i3 is provided with arounded or looped portion 2i designed to be supported between the endsof set screws 22.

The strip l3 has its edges provided with laterally extending pivotmembers 23 designed to be supported in bearings 24 carried by one end ofa spring 25. The opposite end of the spring 25 is connected to the baseill by means of a pivot 26. A set screw 21 is mounted in a suitablesupport 28, and so positioned that downward pressure may be applied tothe spring 25 at a point intermediate the pivot members 23 and 26 insuch a manner that longitudinal pressure may be applied to that portionof the strip i3 between the pivots 23 and the hub l2, tending to bucklethe central portion of the strip from a position within the pressureaxis extending through the pivots 23 and I2.

The inner face of that portion of the strip between the members I2 and23 is formed of a material 29 having a lower co-efiicient of expansionthan that of the material of the strip I3.

The operation of this form of my switch is as follows:

Assuming that the parts are set in the position illustrated by solidlines in Figure 1, and that an increase in temperature takes place, thenthe strip I3 will expand faster than the adjoining member 29, causingthe thermostatic element formed by said strip to straighten and to moveinto the axis of pressure between the members 23 and I2. The lower endof the strip I3 will then move in the opposite direction from thethermostatic strip or in a direction as viewed in Figure 1.

The movement of the thermostatic element and the lower end of the memberI3 is gradual until the thermostatic strip approaches the axis ofpressure. Upon further rise in temperature the said strip will have atendency to bend in the opposite direction, after which rapid movementwill take place and the strip moved to the dotted line position shown inFigure 1, due to the buckling action caused by the compression strainimparted by the member 25.

As the lower end of the member I3 is operated through its initialportion of movement, the member I5 will follow the contact I4 due to theresiliency of the spring I6 until the spring I6 engages the inner end ofthe set screw 20, which takes place at the time the rapid movement ofthe thermostatic element, so that a rapid separation of the contacts I4and I5 is accomplished, and a substantially constant pressure maintainedbetween said contact members during the initial part of the movement ofthe thermostatic strip. As the temperature is lowered, a reverseoperation of the thermostatic strip and the contact members will beaccomplished.

The yieldable member provides means whereby an amplified movement of thecontact member I4 is accomplished over what might be accomplished if themember 23 were carried by a fixed support, thereby providing meanswhereby a large separation may be provided between the contacts I4 andI5.

The set screws 22 provide means whereby the tendency of the thermostaticstrip to assume either one of its oppositely bowed conditions may beincreased or decreased as the adjustment of the set screws will impartto the thermostatic strip a bending strain. 7

The set screw I8 providesmeans whereby the working pressure between thecontacts I4 and I5 may be varied at the will of the operator to meet theworking conditions of the switch. A conductor may be connected to thespring I6 to form one part of an electrical circuit, while a conductor3| may be connected to the member 25 to form the other conductor of saidelectrical circuit. The set screw 20 provides means for adjusting thecritical point of the movement of the member I3, at which the separationof the members I4 and I5 takes place.

In Figures 3 and 4 I have illustrated another form of electrical switchin which the numeral 33 indicates the base having brackets 34 and 35supporting thermostatic strips 36. The ends of said strips are designedto rest on the bulged portion 31 formed in a flexible element 38,preferably in the form of a narrow strip of thin sheet metal.

One end of the element 38 is also secured to the bracket member 35.

One end of the element 38 is provided with an electrical contact member39 designed to engage a coacting contact member 40 carried by a spring4|, supported by a bracket 42. A conductor 43 is connected to saidspring while the conductor 44 is connected to the element 38. A setscrew 45 is designed to engage the spring M for varying the pressurebetween the contact members 39 and 40. Set screws 46 are provided forplacing tension on the thermostatic elements 36, whereby the switch maybe adjusted to operate at different temperatures.

The base 33 is also provided with a support 41 having a set screw 48,the central portion of which is provided with a head 49 fixed thereto.The inner end of the set screw supports a compression spring 50, one endof which is designed to engage the outer surface of the bulged portion31. The tension of said spring is varied by the set screw 48.

The operation of this form of my invention is as follows:

Assuming that the parts are arranged in the manner illustrated by solidlines in Figure 1, and that the temperature is increased, then the freeends of the members 36 will be bowed downwardly as indicated by dottedlines, causing pressure to be applied to the bulged portion 31.Continuing the increase in temperature, stresses will be set up in themember 31 to overcome the rigidity of the member 31, at which time thecentral portion of the member 31 will be rapidly bulged downwardly asindicated by dotted lines, causing the free end of the member 38 to beelevated and with it the contact member 39.

The contact member 4|] follows the contact member 39 through the initialpart of its movement, said movement being limited by a stop 5i, so thata rapid separation of the contacts 39 and 40 will take place as the freeend of the member 38 is snapped upwardly.

This form of my invention differs somewhat from the form beforedescribed in that the member 31 assumes the dotted line position underconstant strain to return to its original position, so that as soon asthe temperature is reduced a small amount, said member 31 rapidlyreturns to its normal position, allowing the contact member 39 torapidly move toward the contact member 40. As soon as the contact ismade between said members then said contact is maintained under uniformpressure due to the resiliency of the spring 40 until its returnmovement is completed.

One difiiculty heretofore experienced in thermostatic switches lies inthe fact that a considerable amount of temperature variation takes placeto cause opening and closing of the switch contacts, due to the slowaction of the flexible elements. I have overcome this difficulty to alarge extent by providing the spring 50 which may have pressure appliedthereto by the set screw 48 and pressure applied to the member 31 bysaid spring to the critical point where the change in shape of saidmember 31 takes place, so that'only a slight movement of the members 36is necessary to overcome the rigidity of the member 31,

thereby providing a narrow temperature variation to accomplish theopening and closing of the switch contact. The temperature at which theswitch contacts may be operated may be varied by the set screws 46.

It will readily be seen that the set screws 46 may be released to suchan extent that the inner ends of the members 36 may be supported abovethe member 31 so that a considerable increase in temperature would haveto take place before the free ends of said members actually engage themember 31, after which a very slight additional rise in temperaturewould cause the switch contacts to open.

In Figures and 6 I have illustrated a slight modification of thestructure shown in Figures 3 and 4, in which the numeral 52 illustratesthe base to which a. bracket 53 is secured, said bracket supportingupright members 54 formed of material having a low co-efllcient ofexpansion.

Supported between the upper ends of the members 54 is a flexible member56 constructed similar to the member 38 and having a bulged portion 56and a contact member 51 carried by its outer end and designed to engagea contact member 58 carried by a spring 59. A set screw 60 is providedfor increasing or decreasing the tension of the spring 59.

Supported in the bracket 53 is a set screw 6| having its upper endprovided with a recess 62 in which is mounted the lower end of a bar 63formed of material having a high co-efllcient of expansion. The upperend of the bar 63 is designed to engage the convex surface of the bulgedportion 56 as shown in Figure 5.

The operation of this form of my device is very similar to that of themechanism illustrated in Figures 3 and 4.

It will be seen that any increase in the temperature will cause themember 63 to expand and lengthen, and cause the member 56 to be bulgedinwardly and the free end of the member 55 to be bent downwardly. Theset screw 6| provides means for applying initial longitudinal pressureto the member 63, whereby a critical pressure may be imparted to themember 56 at any predetermined temperature, thereby providing meanswhereby the temperature variation necessary to accomplish the openingand closing of the contacts 58 may be reduced to a minimum.

Thus it will be seen that I have provided an improved thermostaticswitch in which a flexible element is employed for imparting quickmovement to contact members of an electric circuit. Said flexibleelement is either in the form of a thermostatic strip or supportedseparately and actuated by temperature controlled means such as anexpanding column or a warping thermostatic strip, and in which theconstant pressure may be maintained between the contact members duringthe initial part of the movement of said flexible element; and in theform illustrated in Figures 1 and 2 means is provided whereby yieldablelongitudinal pressure may be applied to the flexible element to increasethe movement of said element as it assumes either of its curvedconditions; and in Figures 3 and 4 means is provided whereby verydelicate adjustment may be made to decrease the temperature variation atwhich the switch points are opened and closed.

The switch mechanism is so constructed as to eliminate excessive wearand bending movement of the flexible elements whereby the life of theswitch may be greatly increased.

The switch is formed of few parts whereby the initial cost of materialis reduced.

I claim as my invention:

1. In a device of the class described, a base, a thermostatic stripsupported thereon, yieldable means for applying longitudinal pressure tosaid strip to normally retain the strip in either of two oppositelyarched conditions and to permit the ends of the strip to separate as itmoves from one of its arched conditions to the other due to temperaturechanges, and adjustable means for imparting a transverse bending strainto a portion of said strip to change the tendency of said strip toassume one of said curved conditions.

2. In a device of the class described, a base, a thermostatic stripsupported thereon, yieldable means for applying longitudinal pressure tosaid strip to normally retain the strip in either of two oppositelyarched conditions and to permit the ends of the strip to separate as itmoves from one or its arched conditions to the other due to temperaturechanges, adjustable means for imparting a transverse bending strain to aportion of said strip to change the tendency of said strip to assume oneof saidcurved conditions, two contact members, means for fixing one ofsaid contact members, and means for operatively connecting the othercontact member to the movable strip whereby the contact member will bemoved to closed or open positions as the arched condition of the stripis reversed.

3. A thermostatic switch comprising a base, a strip of flexible materialhaving a laterally bulged portion near one end, and means for securingthe last end of said strip to said base, contact means carried by thefree end of said strip, a coacting contact member, yieldable means forsupporting the last contact member in contact with the first member,means for adjusting the tension of said yieldable means, and temperatureoperated means for applying pressure laterally to said bulged portion.

4. A thermostatic switch comprising a base, a flexible thermostaticstrip, means pivotally supporting one end of said strip to said base,means pivotally supporting the opposite end of said strip and forapplying yieldable longitudinal pressure thereto to cause the centralportion of said strip to tend to buckle laterally, each end of saidstrip having portions extending beyond said pivot members, a contactmember carried by the free end of one of said extending portions, acoacting contact member, yieldable means supporting the last contactmember, means for adjusting the tension of said yieldable means, meansfor limiting the movement of the last contact member, and means foradjusting the free end of the other extension portion of saidthermostatic strip to increase or decrease the tendency of thethermostatic strip to buckle in either direction.

5. A thermostatic switch comprising a base, a flexible thermostaticstrip, means pivotally supporting one end of said strip to said base,means pivotally supporting the opposite end of said strip and forapplying yieldable longitudinal pressure thereto to cause the centralportion of said strip to tend to buckle laterally, one end of said striphaving a portion extending beyond its corresponding pivot member, acontact member carried by the free end of said extending portion,

a coacting contact member, yieldable means supporting the last contactmember, means for adjusting the tension of said yieldable means, andmeans for limiting the movement of the las contact member.

6. A thermostatic switch comprising a base, a flexible thermostaticstrip, means pivotally supporting one end of said strip, a yieldable andtransversely arranged pressure applying strip supported with one endadjacent to the opposite end of said thermostatic strip, means pivotallyconnecting the adjacent ends of said strips, means for supporting theother end of said yieldable strip to said base, and an adjustable meansfor increasing or decreasing the lateral stress of said yieldable stripas applied longitudinally to said thermostatic strip.

7. A thermostatic switch comprising a base, a flexible thermostaticstrip, means pivotally supporting one end of said strip to said base,means pivotally supporting the opposite end of said strip and forapplying yieldable longitudinal pressure thereto to cause the centralportion of said strip to tend to buckle laterally, said means comprisinga strip of transversely arranged yieldable material having one endpivoted to the yieldably supported end of said thermostatic strip, andits opposite end pivoted to said base, and a set screw supported by saidbase having one end engaging the strip of yieldable material, wherebythe longitudinal pressure as applied to the thermostatic strip may beincreased or decreased.

8. A thermostatic switch comprising a base, a flexible element adaptedto suddenly change its shape when a predetermined pressure is appliedthereto, contact members, means operated by the sudden movement of saidflexible element for moving one of said contact members toward or fromthe other, adjustable means controlled by the temperature variation forapplying or releasing the predetermined pressure as applied to saidflexible element, and means separate and independent of said temperaturecontrolled means for applying yieldable initial pressure to saidflexible element to act in unison with the pressure applied by saidtemperature controlled means to decrease the temperature variationnecessary to open and close said contacts, and means for adjusting thepressure as applied by the initial controlling means.

9. A thermostatic switch comprising a base, a

flexible element adapted to suddenly change its shape when apre-determined pressure is applied thereto, means for mechanicallyapplying an initial pressure to said element, tending to deform thesame, contact members, means actuated by the element as it changes itsshape for moving one of said contact members toward or from the other,temperature controlled means for applying pressure to said element toassist the initial pressure applying means whereby the element willsuddenly change its shape when the combined pressure of the first andsecond pressure applying means is equal to the pre-determined pressure,and means for adjusting the first and second pressure applying meansindependently whereby the temperature variation necessary to open andclose said contacts may be decreased.

CLARENCE R. LAUBENFELS.

